通过会员类，你可以创建用户并管理他们，每一个用户都由一个会员类的实例所代表。

From the Membership class, you can create and manage users, each of whom is represented by an instance of the MembershipUser class.

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在此例中，你将会在你的图表中为此前建模的每个工具类创建一个用例，以后它们就代表我们系统的主要功能。

In this example, you will create a use case in your diagram for each of the previously modeled utility classes, since they represent the main functionality of our system.

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你可以把这个类想象成代表了一个实际的文档，比如一个html页面，一个PD f文档，或者一个文本文件。

You can think of this class as a virtual document, such as an HTML page, a PDF file, or a text file.

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